Breakdown of Lögreglan stoppar hann af því að hann er án bílbeltis.
vera
to be
hann
he
af því að
because
stoppa
to stop (moving) / to stop (someone/something)
Questions & Answers about Lögreglan stoppar hann af því að hann er án bílbeltis.
Why does the word for seatbelt end in '-s' here?
Because of the preposition án (without). This preposition requires the noun that follows it to be in the genitive case. The base word is the neuter noun bílbelti, and its genitive form takes an -s at the end, making it bílbeltis.
In English, 'police' is treated as a plural word ('the police stop him'). Is it plural in Icelandic too?
No, in Icelandic, lögreglan is a singular feminine noun. You can see this because the verb stoppar is in the singular form. The -n at the end of lögreglan is the attached definite article, meaning 'the'.
Why does it take three words (af því að) to say 'because'?
That is simply the standard Icelandic phrase for 'because'. It literally translates to 'of it that', but you should just memorize af því að as a fixed chunk. In casual spoken Icelandic, you will often hear it shortened to því að or just því.
Why is the word hann used for both 'him' and 'he' in this sentence?
For the masculine pronoun hann, the nominative case (used for the subject 'he') and the accusative case (used for the object 'him') happen to be exactly the same word. The first hann is the object being stopped, and the second hann is the subject who is without a seatbelt.